Velocity of cart after seperation

[jimmyly]

Homework Statement

Hello, so i had a family party and my cousin was doing his physics homework so i decided to join in. now I'm at home and was playing with one of the problems that his teacher didn't assign and got an answer that i want to check because my teacher skipped the moment chapter(i go to community college and we ran out of time because we had a strike) so i really want to know if i got it.

i can't remember what exactly the question said but i remember my sketch

[m1]--[m2]-->4m/s
cart 1 and cart 2 are connected as a train going 4m/s

[m1]- *break* -[m2]-->7m/s
cart 1 cart 2
what is the velocity of cart 1

Homework Equations

P=mv

The Attempt at a Solution

P = mv

p=p' because of conservation of momentum?

p = m1v1 + m2v2
v1 = (p - m2v2)/m1
this is where I'm kind of iffy... if together they go 4m/s does that mean they both go 4m/s or is it divided by 2 each?

 

[jimmyly]

now I'm thinking... if i need a ratio between the two masses?

 

[jimmyly]

okay i just realized i use v2=7m/s for v1= (p - m2v2)/m1... lol